Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $46.26   4.662%   $48.4166   $48.42   $48.40   $48.40  
  Purchase #2 $71.55   6.162%   $75.9589   $75.96   $75.95   $76.00  
  Purchase #3 $108.36   10.709%   $119.9643   $119.96   $119.95   $120.00  
  Purchase #4 $249.80   6.619%   $266.3343   $266.33   $266.35   $266.30  
  Purchase #5 $14.88   7.122%   $15.9398   $15.94   $15.95   $15.90  
  Purchase #6 $72.44   6.603%   $77.2232   $77.22   $77.20   $77.20  
  Purchase #7 $58.97   6.213%   $62.6338   $62.63   $62.65   $62.60  
  7 purchase totals = $622.26       $666.4709   $666.46   $666.45   $666.40